Separation and characterization of urinary glycosaminoglycans of kidney stone formers and normal individuals

Since the depth of surface-breaking cracks often determines the remaining life of a part, the characterization of surface-breaking cracks is a key problem in nondestructive evaluation. Eddy currents have been used for this purpose [1]. However, traditional eddy current methods have poor success when the dimensions of the crack are small compared with the inner radius of the eddy current probe. This is as expected, since the spatial resolution of an eddy current probe is comparable with its inner radius. Moulder et al [2] and Nakagawa [3] have described a new eddy-current based method of nondestructive evaluation, known as the photoinductive method. It offers greatly enhanced spatial resolution by combining the eddy current method with a laser. Images made with the photoinductive method provide a map of the surface-breaking portion of the crack and directly measure its length along the surface. In essence, the photoinductive method allows one to map the square, E · E, of the electric field, E, on the surface of the metallic part. In this paper, we develop and present a new method for estimating the depth and the shape of surface-breaking cracks in metallic parts from photoinductive data

Forward and Inverse Processing in Electromagnetic NDE Using Squids

Electromagnetic NDE has been successfully applied to the detection of surface cracks and is routinely used to locate flaws in airframes, pipelines and in steel offshore oil platforms. However, there are still many problems to be solved, particularly in the aviation industry, which require the detection of deeper flaws such as corrosion in multi-layered structures and cracks around rivet holes which are obscured by the head of the rivet. Most systems use coils as detectors (though Hall probes are occasionally used), which have low sensitivity at low frequencies due to the fact that the induced voltage is proportional to the rate of change of magnetic flux through the coil. Unfortunately it is necessary to use low frequencies to detect deep subsurface flaws on account of the skin-depth effect, otherwise the electromagnetic field cannot propagate down to the depth of the flaw. SQUID (Superconducting Quantum Interference Device) sensors are ideally suited to overcome the deficiencies of coils, because they are primarily detectors of magnetic flux which, together with their high sensitivity, makes the detection of deep flaws more likely. SQUIDs have been successfully used for measuring very low magnetic fields, particularly in the field of biomagnetism, and it is hoped to exploit this sensitivity to detect flaws at large stand-off distances for example in pipelines which are surrounded by thick layers of cladding